A conventional networked computer system is comprised of a number of computers that each have an operating system, a network for communicating data between the computers, and at least one data storage device that is attached to at least one of the computers but not directly attached to the network. In such a system, the transfer of data between the data storage device and a computer in the system other than the computer with which the device is associated requires that the operating system of the computer with which the data storage device is associated to devote a certain amount of time to the processing of the data transfer. Because the operating system of the computer is typically servicing requests from various applications (e.g., a word processing application) executing on the computer, the operating system typically is only able to devote a limited amount of time to the processing of the data transfer.
While data transfer rates over networks were relatively slow, the operating systems were typically able to service data transfer requests quickly enough to utilize any available time on the network for data transfers between computers in the system. In other words, the networks, due to their relatively low transfer rates, were the bottleneck in transferring data between a data storage device associated with one computer in the system and other computers in the system. However, as the data transfer rates for network improved, the operating system became the bottleneck because the operating system was typically servicing requests from various applications when the network was available for data transfers to or from the data storage device.
To avoid the operating system bottleneck, data storage devices were developed that directly attached to a network, i.e., network data storage devices. Due to this direct attachment, any computer in a networked computer system is able to directly communicate with the network storage device.
A further advent has been the development of distributed network data storage in which two or more network data storage devices are utilized and a mechanism exists for defining a logical volume, i.e., a unit of data storage that physically extends over the two or more data storage devices. Consequently, to computers in a networked computer system, the logical volume appears to be a single storage device. An example of a network computer system that employs distributed network storage is comprised of: (a) two fibre channel disk drives; (b) a computer; and (c) a network for facilitating data transfers between the drives and the computer. The computer comprises a driver (a program that allows an operating system to communicate with a device) for each of the drives and a logical volume manager that controls the drivers so as to define a logical or virtual volume that extends over the two fibre channel disk drives.